Hi

Your amp doesn't have an FX loop - none of the Spider series do except Spider Valve, so the only way you can use other pedals is to use them between the guitar and the amp's input - which is the ideal place for an Ibanez Tube screamer anyway.  Remember though that your amp is a modelling amp and as such it already has a number of distortion and overdrive type FX so whilst a Tube Screamer pedal should enhnace the capabilities of the amp it may not necessarily behave quite the same as it would with a non-modelling amp, but in essence, yes you can pretty much use any pedals you like with your amp

Nick